1. Field of the Invention
The invention relates to form a capacitor structure of a semiconductor, more particularly the method is completed by improving the thickness of the silicon nitride layer.
2. Description of the Prior Art
In the prior art, first of all, as FIG. 1A, an atmosphere-pressure oxide layer 121 is deposited onto the surface of a semiconductor substrate 120. Especially, there are cells 150 formed into the semiconductor substrate 120 already. Then, a silicon nitride 122 is formed on the surface of the atmosphere-pressure oxide layer 121. Again, a low-pressure oxide layer 123 is formed on the surface of the silicon nitride 122. Then, a first photoresist 161 is formed onto the first nitride layer 123 to define a polysilion dielectric layer 181.
Consequentially, as FIG. 1B, a portion of the low-pressure oxide layer 123, the nitride layer 122 and a portion of the atmosphere-pressure oxide layer 121 are all etched as columns using the conventional dry etching to form an opening 181. These columns will conclude the low-pressure oxide layer 123, the nitride layer 122 and the atmosphere-pressure oxide layer 121.
Then, as FIG. 1C, by the chemical vapor deposition, the first polysilicon layer 124 is formed on the surface of the low-pressure oxide layer 123 and is filled up into the first opening 180 and is covered on the low-pressure oxide layer 123. The second photoresist 162 is formed on the polysilicon layer 124 to define the opening of the polysilicon via.
As the FIG. 1D, the portion of the first polysilicon layer 124 is etched using the dry etching to form a bottom plate of the capacitor. Here, the photoresist layer 162 is used as an etch mask.
Next, as FIG. 1E, a silicon nitride layer 125 is formed on the surface of the polysilicon layer 124 using the chemical vapor deposition. The thickness of this silicon nitride layer 125 is about 50 angstroms. There is the topographic effect happened on the silicon nitride layer 125, such as legend 10. This topographic effect will seriously damage the function of cell.
As FIG. 1F, the wet oxidation layer 126 is deposited onto the silicon nitride 125 using the wet chemical deposition to form the top plate 127 of the capacitor. Therefore the capacitor structure is completed.
In the incubation time of the process, the thickness of nitride deposited on the oxide is thinner than the nitride deposited on the silicon. While the thickness of oxide-nitride-oxide layer is reduce, the topographic effect of the thin nitride deposition in the process will make the nitride thickness between the silicon and inter-polysilicon dielectric boundary becomes too thin, also this withstands the following wet oxidation process. At this time, grain boundary oxidation may occur at the neck of polysilicon via, which results in abnormal increment of node contact resistance.